1. Technical Field
The present disclosure relates generally to a fuel cell system, and more particularly, to a fuel cell system which may reduce the volume of the fuel cell system by decreasing thickness of a stack.
2. Description of the Related Art
A fuel cell system is a power generation system for converting chemical energy from a reaction between an oxidant and hydrogen contained in a fuel, for example, a hydrocarbon-based material such as methanol, ethanol, and natural gas, to electrical energy.
Examples of fuel cell systems include polymer electrolyte membrane fuel cell (hereinafter, referred to as “PEMFC”) systems and direct methanol fuel cell (hereinafter, referred to as “DMFC”) systems.
Generally, a PEMFC system comprises a stack that generates electrical energy in a reaction between hydrogen and oxygen, and a reformer that generates hydrogen by reforming fuel. The PEMFC system typically has a high energy density and a high output, but uses hydrogen as the fuel and uses accessory devices such as a fuel reformer to generate the hydrogen fuel by reforming methane, methanol, and natural gas.
On the other hand, the DMFC system produces electricity by a direct electrochemical reaction between methanol as the fuel and oxygen as the oxidant. The DMFC system typically has a high energy density and a high electrical power density, and because it directly uses a liquid fuel such as methanol, accessory devices such as reformers are not required. Storage and supply of fuel is easy.
In the PEMFC and DMFC, the electricity generating stack substantially comprises a plurality of membrane electrode assemblies (hereinafter referred to as “MEA”), and separators or bipolar plates sequentially stacked. The MEA comprises a membrane interposed between an anode electrode and a cathode electrode. Accordingly, the stack of the PEMFC system and the DMFC system comprises a separator interposed between an anode electrode and a cathode electrode of two adjacent MEAs facing each other and stacking these components together. The separator has a fuel flow path formed on one side thereof and an air flow path formed on the other side thereof, which supplies the anode electrode and the cathode electrode with externally supplied fuel and air.
The thickness of the stack is determined according to the number of MEAs and separators, and the respective thicknesses of the MEAs and the separators. Where the number of MEAs and separators is large, the thickness and volume of the stack increases to the point that the stack cannot be used in portable systems.